Today, increasing demands for processing liquids are present. The processing often involves biological treatment of liquids such as wastewater, semiliquid manure etc. Various attempts have been made to optimise processes for biological treatment of liquids e.g. as presented in WO 9603351.
US 2002/0185418 A1 discloses s biological reactor process for continuous purification of wastewater by converting its constituents to a solid form that can be easily separated using retainable biological catalysts and a novel reactor. The reactor comprising a reaction vessel and at least one draft tube open at both ends and mounted on a bottom of the vessel. Inside the vessel, a circulatory flow is established as well as a bed of bio carriers. However, the exposure of wastewater to the bio carriers are found limited due to the formation of a bed, and it is found that a zone is created inside the reactor where no or limited flow occurs.
WO 2007/058557 discloses an apparatus for high rate anaerobic treatment of (waste)water with relatively high concentrations of lipidic compounds. In a container, influent is fed from the top and the container is equipped with a separation step at the bottom. Reactor contents are thoroughly mixed by a combined action of a gas lift loop and a liquid recycle over the reactor. The gas lift is called a “natural gas lift” and is provided by internal biogas production without the infeed of gas from a compressor or pump. However, the system has been found to operate slowly thereby being less effective.
One of the drawbacks in the known systems is flow regions with stagnant or very limited flow established, resulting in that the overall efficiency of the systems decreases. Furthermore, too high flow velocity inside the containers used may destroy the bio-film on the bio-film carriers, thereby limiting the cleaning effectiveness, and a too low flow velocity may result in the bio-films growing too much. Furthermore, in systems where gas such as air is to be inputted, there is often a problem related to efficient oxygenation of the liquids.
In addition to the above, it is often desireable to have a vivid motion of the bio-film carriers inside the container which motion should preferably include the individual bio-film elements not moving as in a fluidised bed configuration, but travelling throughout the entire volume of the container in which the bio-film elements are contained. Creation of such a vivid motion gives rise to at least two inter-connected problems (as untreated fluids have to enter the container, and cleaned fluids have to be extracted from the container), namely creation of the motion and extraction of liquids. This can be disclosed as the hydraulic load, HL, e.g. defined as a characteristic velocity squared, i.e. HL≈U2. In treatment systems aimed at by the present invention, the hydraulic load internally in the container should be high, whereas the hydraulic load on outlet (used to withdraw liquids from the container) should be considerably lower in order to prevent the withdrawal of liquids from the container from destroying, dictating or influencing the vivid motion aimed at the inside the container.
GB 2 315 264 discloses a wastewater treatment apparatus having a granular carrier separating duct and an outlet duct for discharging treated wastewater. However, the carrier separating duct and the outlet duct are arranged in a manner forcing the granular carriers downwardly while allowing fluids to move upwardly towards a weir behind which the outlet duct is provided. The separation of the liquids from granulates is thereby provided by gravitational/momentum forces, and the flow inside the container is highly influenced by the carrier separting duct and the outlet duct.
EP 2 394 966 discloses an apparatus for retention of (bio)solids for use in wastewater treatment. The apparatus disclosed comprising a vertically elongated effluent compartment equipped with two or more hoods connected to one or more riser tubes being open at the top and equipped with sludge deflection plates. The effluent compartment being equipped with a treated wastewater outlet system at the top part of the effluent compartment comprising one or more overflow wiers. The concept behind the device disclosed is that sludge rised through the hoods (due to gas lifting action) upwardly towards a deflection plate, pass the weir and into the outlet. While sludge is disclosed as moving upwardly and into the hoods, sludge is also recycled downwardly. This counter current recycling and gas lifting action highly limits the motion inside the container to very low velocities as higher velocities would otherwise destroy the gas lifting action. Thus, the device in EP 2 394 966 is only capable of producing a flow with a low hydraulic load.
WO 9603351 discloses an attempt to improve the efficiency of a biological treatment process. The process disclosed takes place in an open ended container with internal flow generation by use of gas addition to generate mixing inside the container. While the process and device disclosed therein indeed is considered as a step towards a more efficient biological treatment process, the process may be seen as still having some critical drawbacks. In the apparatus disclosed, the collection of treated water is performed through a single outlet provided in the container wall, at a position below the upper end of a centrally arranged tube. A slanted screen is provided in front of the outlet. This arrangement may have a tendency to skew the flow inside the reactor to an extend that could generate regions of stagnating flow (regions where no flow occurs).
US 2012/0152831 discloses an apparatus for cleaning wastewater. The apparatus comprises a throughput tank having a filler material to which microorganisms are adhered and wherein the throughput tank is ventilated with an oxygen containing gas. The inflow of wastewater into the throughput tank and the ventilation of the throughput tank is affected from bottom of the throughput tank and in such a gas amount, that the wastewater and the filler bodies suspended therein are mixed and the microorganisms on the filler bodies are supplied with sufficient oxygen. On the upper circumference of the throughput tank, drainage slits for the cleaned wastewater are provided. An overflow weir is also provided at the upper circumference of the throughput tank which weir surrounds the throughput tank at the upper end below the drainage slits like a collar. The apparatus is well suited for used with filler bodies being suspended in the fluid (the density of filler bodies and fluid are substantially equal). If a vivid up-downwardly motion of the filler bodies is realised, this would result in the volume flow through the weir becoming uncontrollable as the volume flow is governed by Q≈LH2/3, where L is the length of the weir and H is the height about the crest. Further, as the apparatus does not allow for any controlled downward motion of the filler material, these filler materials would be dragged towards the weir potentially blocking the wier over time.
Hence, improved methods, devices and systems for biological treatment of liquids such as water would be advantageous, and in particular more efficient and/or reliable methods, devices and systems would be advantageous.